Known in the art is the impeller of a centrifugal compressor comprising the main disc, blades and a covering disc which consists of a web to effect gas flow in the impeller and a ring to accomodate seals (V.F. Ris. Centrifugal Compressor Machines, 1981, Mashinostroenie Publishers, Leningrad, pp. 35, 103).
The covering disc is made solid from one forging. The impellers with such covering discs feature the possibility of operation at high circumferential velocities (from 120 to 300 m/s).
However, the making of covering discs solid from one forging calls for substantial consumption of metal (metal utilization factor is 15%) and great labour intensity (85% of metal turn into chips).
Besides, high circumferential velocities give rise to flexural strain of the ring and the web, as well as radial strain of the ring. These strains bring about radial movement of the ring which calls for larger clearances between the ring and the seals mounted in the compressor body. The larger the clearances, the greater are gas leakages and the lower is the compressor efficiency.
There is known in the art a centrifugal compressor impeller, comprising the main disc, blades and a covering disc made up from the web for effecting the flow of gas in the impeller and the ring for accomodating the seals, both the web and ring being interconnected. (cf. A. D. Bruk. Smoke Exhausters of Gas Purification Facilities. 1984, Machinostroenie Publishers, Moscow, p. 120).
The ring is connected to the web either through welding or rivetting. The impeller in which the covering disc is made composite with such a connection of the web to the ring features lesser labour and metal intensity compared with that in which the disc is solid, but higher stress in the web-ring joint making it impossible to use such impellers in case circumferential velocities are greater than 120 m/s.